This invention relates, in general, to a method of processing semiconductor materials, and more particularly, to a plasma processing method for a high resistivity substrate such as gallium arsenide (GaAs).
During plasma processing, such as plasma etching or plasma enhanced chemical vapor deposition (PECVD), high resistivity substrates show a significantly higher nonuniformity across the surface of the substrate as compared to low resistivity substrates. This nonuniformity can be characterized into two major types. One, a gross nonuniformity across the entire front surface of the substrate, and two, localized nonuniformities at certain portions at the front surface of the substrate due to a replication of the features from the transfer assembly. These features may include lifter pin marks or backside He cooling channels in the lower electrode.
For example, the surface of a GaAs substrate after oxide deposition may be 1% nonuniform. However, after plasma etching, the nonuniformity of the surface may rise to over 15%. Further, as the diameter of the substrate increases, the surface nonuniformity substantially increases.
Surface uniformity, which means the uniformity of the etch process or deposition process, is critical for fabricating devices with minimal process damage. By significantly improving the gross uniformity across the front surface of the substrate and by eliminating localized areas of nonuniformity, yields can be improved and device performance reliably optimized.
Accordingly, it is highly desirable to have a method for improving surface uniformity across the surface of a substrate during plasma processing and eliminating the problems associated with nonuniformity.